Disorders to parturition currently constitute the single most important problem in child health. Indeed, it is estimated that preterm labor alone accounts for greater than 75% of the perinatal morbidity and mortality seen in this country each year. The long-term objectives of this application are to elucidate the mechanisms by which labor is initiated in pregnant women and to develop methods to prevent the premature initiation of parturition. The specific aims in this proposal are intended to define the cellular and molecular mechanism s by which a well-characterized hormone, oxytocin, mediates uterine contractility. WE propose to isolate and purify the uterine oxytocin receptor and to generate high-affinity polyclonal antibodies to the receptor for use in biochemical, morphological and molecular analysis of receptor function. Using both biochemical and immunoelectron microscopic techniques we shall define the cellular life cycle of the receptor including its biosynthesis, processing, intracellular traffic and membrane topology and we shall define the kinetics and pharmacology of oxytocin binding, signal transduction and degradation. We further propose to clone the uterine oxytocin receptor and thus determine the receptor sequence and molecular structure. We shall express the cloned receptor in mammalian fibroblasts and use site-directed mutagenesis to define the molecular anatomy of receptor structure and function and to characterize the molecular details of receptor cell biology. Finally, we shall use the receptor clones to identify the cell-type(s) expressing the oxytocin receptor in the gravid uterus and to elucidate the mechanisms of receptor gene expression in the uterus during gestation and parturition. The data from these studies should allow us to construct a working model of the basic mechanisms by which uterine contractility influenced by oxytocin. Taken together with new information on other hormones and agents mediating uterine contractility we anticipate that this work will lead to a clearer understanding of the biology of human parturition and allow the development of rationale scientific methods to prevent premature labor.